There have been many advances in art of electronic control of scale weighing systems. It is desirable to be able to electronically control a scale system, which, for example, may be utilized for the automatic weighing of liquid or granular materials being placed into packaging containers. Further, it is desirable to be able to adapt such an electronic control to a presently existing mechanical scale in order to avoid the expense associated with replacing an item of capital equipment which has not reached the end of its service life. This invention relations to particular electric circuitry and mechanical apparatus utilized for the conversion of a mechanical scale system to an electronically controllable scale system.
It is common, in the conversion of a mechanical scale to one that is automatically controlled by electric circuitry, to replace the entire scale head, a conversion which involves considerable expense. Another popular method of conversion used is to fit a mechanical scale head with a reed switch and magnet. The magnet, being fitted on the scale pointer, may open or close a contact of the reed relay as the pointer passes the switch. Such a system suffers from the inherent limitation of the number of such switch and magnets that can be fitted onto the dial of a mechanical scale. Having a finite number of reed switch and magnet relays necessarily limits the number of points which may be selected for cut-in or cut-off weights for the weighing system.
Another sometimes employed method of converting a mechanical scale to an electronically controllable scale is to mount a device which senses inclination of the internal scale parts on, for example, the fifth lever of the scale, or to cut the steelyard rod and insert a load cell at the opening. A inclinometer or load cell is, of course, a transducer, which must be attached to the electronic circuitry of the scale controller by means of connecting wires. Such an arrangement inhibits the accurate functioning of very sensitive scales since there is usually some contact between the moving parts and the non-moving parts of the scale, at least in the form of the wires which connect the transducer to the circuitry of the controller.